In a role reversal from their eight years together in the White House, Barack Obama has become Joe Biden’s wingman and, in his understated way, his hatchet man.

The former president’s Thursday eulogy for the late Rep. John Lewis, a Georgia Democrat who was active in the civil rights movement, was a case in point. Obama criticized President Trump and reminded Democrats who they would be letting down if they didn’t elect Biden and a Democratic Senate, urging them to jettison the filibuster — a key institutional obstacle to liberal ambitions — as a “relic of Jim Crow.”